In general, washing machines remove dirt from clothing or beddings (hereinafter, referred to as “laundry”) using mechanical interactions between water, detergent, and laundry. A washing machine performs washing, rinsing, or dehydrating operations to clean the laundry.
Washing machines include agitator-type, pulsator-type, and drum-type washing machines.
An agitator-type washing machine includes a washing rod at a center of a washing tub. The washing rod swings left and right for washing the laundry. A pulsator-type washing machine includes a plate-shaped pulsator at a lower portion of a washing tub. The pulsator rotates left and right to cause a friction between water and laundry so that the laundry is washed by the friction. A drum-type washing machine includes a drum to contain water and laundry. Washing is conducted by rotating the drum.
A drum-type washing machine includes a cabinet configuring the appearance, a tub in the cabinet to contain water, a drum inside the tub to receive laundry, a motor at a rear side of the tub to rotate the drum, and a drive shaft that is connected to a rear side of the drum through the motor and the tub. A lifter is provided inside the drum to lift the laundry when the drum rotates.
When the washing machine operates, laundry tends to be easily tangled so that laundry is biased to a side (generally referred to as “eccentricity”). As the drum rapidly rotates with the laundry biased (for example, upon dehydration of the laundry), an unbalance occurs between a geometrical center of the rotational shaft of the drum (also referred to as “center of rotation”) and a real center of gravity of the drum, thus causing vibrations and noise. To reduce vibrations and noise, a balance is installed that mitigates the unbalance.
Counter weights have been used as balancers for drum-type washing machines. A counter weight provides additional weight to calibrate eccentricity. Recently, ball balancers are being widely employed for washing machines. A ball balancer has a ring-shaped space circumferentially installed at a front or rear side of a drum to have a predetermined width. A ball and a liquid are filled in the space and thermally bonded to each other to tightly seal the space. As the drum rotates at high speed, the balancer causes its inner materials to be moved away from the center of gravity of the laundry so that the overall center of gravity of the drum approaches the center of rotation.
Such a balancer-adopted washing machine has a time period of rotating the drum at a predetermined speed before high-speed spinning. Then, an unbalance value of the drum is calculated from a variation in rotational speed of the drum. The drum is accelerated at an appropriate acceleration time is determined based on the unbalance value. However, the unbalance value may vary with temperature of the balancer, thus leading to a wrong acceleration time.